Progress in FY2017 was in the following areas: SEGMENTAL LABELING OF HIV-1 CAPSID ASSEMBLIES: We have developed an intein-based protocol for producing the HIV-1 capsid protein (CA) with 15N,13C-labeling of either the N-terminal domain (NTD) or the C-terminal domain (CTD), and with high yield. CA assemblies formed in vitro from segmentally labeled products have greatly simplified 2D and 3D solid state NMR spectra, due to alleviation of spectral congestion. Segmentally labeled assemblies will be used to characterize intermolecular NTD-CTD interfaces and other local structural details within the mature HIV-1 capsid lattice. A paper describing these results is in preparation.